In modern-day industry or engineering, a hole saw will generally be used to make round holes in various materials such as metal. Motive power must be provided to the hole saw during this process of saw cutting, therefore the hole saw is generally mounted on an electric tool such as an electric hand drill, percussion drill or radial drill for use therewith. To adapt to different hole saws and different electric tools, a mandrel assembly for providing connection and transmitting torque is generally disposed therebetween.
On the one hand, the coupling of a conventional mandrel assembly to a pilot drill, and the coupling of a conventional mandrel assembly to a hole saw, are usually accomplished by screw-thread fastening. It is time-consuming and laborious to fit the pilot drill and the hole saw to the mandrel with this coupling method, and replacement of the pilot drill and hole saw is inconvenient.
On the other hand, a conventional quick-fit mandrel assembly achieves quick fitting of a pilot drill and hole saw, but these quick-fit systems often mostly have a polygonal fit. This method of fitting can not only transmit twisting force but also achieve guiding; moreover, the processing precision thereof is low, and this will result in a large fitting gap. There is considerable rocking during formation of the hole, and this has an impact on use.
Specifically, a mandrel assembly of a conventional quick-fit system comprises components and parts such as a mandrel, an adapter and a bit coupler, and a screw-thread connection or hexagonal fit connection is mainly used between the various parts therein. When a pilot drill and a hole saw are mounted on the quick-fit system, there will be a very large fitting gap and mounting will not be coaxial, hence considerable vibration will arise during the process of hole formation, and this will have an impact on the hole-forming quality and service life of the hole saw. As a practical example, in a certain electric tool, a screw-thread connection is generally used between a mandrel thereof and a bit coupler, and there is no guiding face; an adapter and the mandrel are connected and guided in a loose hexagonal fashion; a bit and the bit coupler are connected and guided in a loose hexagonal fashion; and a hole saw is connected to the adapter by screw-threads. The loose hexagon fit at two positions in this electric tool result in a larger fitting gap, so considerable vibration occurs during the actual process of hole formation.
As the length of the structure of the hole saw itself increases, the abovementioned problem becomes more serious. For example, when it is used to cut metal, a pilot drill is unable to center the hole saw, so the hole saw will vibrate violently, resulting in very poor cutting quality. On the one hand, saw marks and scrapes with a very large span occur on the metal cutting face; this means that the hole saw is swinging throughout the operation and lacks good guidance. On the other hand, the bit of the pilot drill is not at the center of a slice; this means that the coaxiality of the bit and the hole saw is poor, so there is a large swinging space between the pilot drill and the hole saw. Furthermore, due to the lack of alignment between a bit and a cutting disk, it is difficult to remove a rejected cutting disk.